The effectiveness of a radiopharmaceutical composition can be improved if the specific activity and purity of a radioisotope is increased. However, specific activity is often limited by the available production methods for the isotope and the subsequent purification procedure. Therefore, a recognized need exists in the art for medically useful radionuclides with high specific activities and purities.
Tin-117m is a useful radioisotope in the field of nuclear medicine. The nuclear-physical and biochemical properties, such as a 14-day half-life, a gamma emission of 158 keV (87%) and a high yield of short-range conversion electrons with energies of 126 keV (64%), 152 keV (26%) and 129 keV (11%), of Sn-117m have been exploited for various bone and joint conditions, including palliative bone cancer treatment.
There are several known methods of producing no-carrier-added (NCA) Sn-117m compositions. For example, reactions utilizing non-tin target atoms may employ proton-induced, 3He-particle-induced, or α-particle-induced reactions on cadmium and indium targets. Reactions, such as 114Cd(3He, γ), 114Cd(α, n), 116Cd(3He, 2n) 116Cd(α, 3n), 115In(d, γ), 115In(3He, p), and 115In(α, pn), are known to lead to the formation of NCA 117mSn. However, in addition to the manner of isotope generation, another major hindrance with producing NCA 117mSn with high specific activity is the absence of an effective method for separating 117mSn from the target material. Separating small quantities of a desired species from a much larger matrix (debulking) is notoriously difficult using conventional separation methods, such as, chromatography or extraction. Historically, this very aspect of radionuclide purification provoked the use of a carrier, thereby rendering samples with reduced specific activity.
U.S. Pat. Nos. 8,257,681 and 8,632,748, which are incorporated herein by reference in their entirety, disclose extraction and chromatography methods for providing high specific activity, NCA Sn-117m compositions from an irradiated cadmium target. Chromatography methods are generally relatively time intensive, as compared to liquid-liquid extraction methods. However, the disclosed extraction method, which utilized a hexone extraction of a hydrochloric acid solution of the etched irradiated cadmium target, provided a Sn-117m product that still contained a substantial residual quantity of cadmium.
Therefore, in view of the foregoing, there is still a need for new methods for producing high purity, NCA, high specific activity 117mSn.